Aerogel is a low-density, nanoporous solid material composed of 50 to  greater than 99% air by volume. Aerogel is typically prepared by supercritically extracting the liquid medium from gel in such a way that the gel""s solid matrix is isolated without collapsing due to capillary forces. Aerogel typically shows densities ranging between 0.5 g/cm3 to 0.001 g/cm3, yet at the same time can support between 500 and 4,000 times its weight in an applied force distributed across its surface area. Internal surface areas in aerogels range from 250 m2/g to 2,500 m2/g, giving them excellent insulative and impact-absorbing capabilities.
Aerogels are prepared by supercritically drying precursor gels called alcogels. A gel is a colloidal system in which a network of interconnected solid particles spans the volume of a liquid medium. In the most researched type of aerogel, silica aerogel, this gel is composed of a silica matrix spanning a solvent such as ethanol or acetone.
Modern aerogel is synthesized by the sol-gel process, in which a metal alkoxide is reacted with water in a polar organic solvent to yield a colloidal system of oligomeric silica clusters suspended in the solvent, or a sol, which, upon further polymerization, forms a gel.
Aerogel was discovered by Samuel Steven Kistler in the 1930s at the College of the Pacific (Stanford University)1. Aerogel was only researched extensively, however, in the 1980s when NASA investigated it as a possible medium for capturing micrometeoroids during space flights. Since then, aerogel production has been significantly improved, and has made aerogel popular in numerous applications industrially, commercially, and in research. NASA used aerogel on the Mars Pathfinder probe to survey the atmosphere of Mars, and has used it on several probes as micrometeor sponge.
1NASA Jet Propulsion Laboratory. Aerogel. March 1996. 
Despite its useful properties, aerogel""s use has been greatly limited by the expense and difficulty of its manufacture. In addition, aerogel""s blue color has prevented it from being usable in applications such as windowpanes and other transparent insulation applications.
Preparation of Alcogel
Silica aerogel, is typically formed by the reaction of a silicon alkoxide with water to form an alcogel through the sol-gel process. Alcogel can then be supercritically dried to leave behind the silica matrix that gave the precursor alcogel its rigidity. The resulting low-density solid material is aerogel. Examples of silicon alkoxides include tetramethyl orthosilicate and tetraethyl orthosilicate.
The formation of the alcogel is the step in which the physical and nanostructural properties of the aerogel are defined. Since the polymer matrix of which the aerogel will be composed is assembled during the gelation process, the chemistry of the alcogel solution can be adjusted to give specific properties to the derivative aerogel.
Silica alcogel will be used as the subject of discussion for chemical reactions, since it is of most relevance to the method of the invention.
The net reaction for the formation of the alcogel is as follows2:
nMe(OR)4+4nH2Oxe2x86x92nMe(OH)4+4nROH Hydrolysisxe2x80x83xe2x80x83(1)
nMe(OH4)xe2x86x92nMeO2+2nH2O Condensationxe2x80x83xe2x80x83(2)
R=alkyl group (i.e. C2H5)
The metal alkoxide reacts with four moles of water yielding hydroxyl groups and four moles of alcohol. The hydroxyl groups then condense to produce a metal oxide and water. This happens in a three-step reaction mechanism2.
xe2x89xa1MeOR+HOHxe2x89xa1MeOH+ROH Hydrolysisxe2x80x83xe2x80x83(1)
xe2x89xa1MeOR+HOMexe2x89xa1MeOMexe2x89xa1+ROH Alcohol Condensationxe2x80x83xe2x80x83(2)
xe2x89xa1MeOH+HOSixe2x89xa1MeOMexe2x89xa1+HOH Water Condensationxe2x80x83xe2x80x83(3)
2Tillotson, Thomas M. and Hrubesh, Lawrence. 
As the reactions occur, the solution forms a sol of silica clusters capped by alkyl and hydroxyl groups. These clusters can be made to interconnect to form a matrix throughout the liquid medium thus forming a gel. This process, known as the sol-gel process, allows for metal oxide to carefully form and interconnect by network-type bonds. After gelation occurs, the alcogel is aged and soaked in an organic solvent for several days to remove any unwanted water, catalyst, and alcohol.
Once an alcogel has been diffused with a pure solvent, preferably a non-alcoholic solvent such as toluene, it can be dried to produce an aerogel. Upon evaporation, like gelatin, a gel will condense into a hard glass-like material. As liquid is evaporated out of the silica matrix of an alcogel, hydroxyl groups lining the edges of the matrix interact by weak hydrogen bonding and stick together. As capillary action pulls the matrix inward, the hydrogen bonding causes the matrix to stick and collapse. There are ways to prevent the solid matrix from collapsing, however, such as supercritically extracting the solvent from the gel.
The supercritical extraction process requires that the gel""s solvent be brought past its critical pointxe2x80x94the temperature and pressure that once reached, the substance cannot condense into a liquid by adding further pressure. Such supercritical fluids have extremely rapid diffusion rates, and possess some properties similar to liquids, such as density, and other properties similar to gases, such as expansion3. Supercritical extraction allows for removal of the liquid solvent from the gel while still providing the physical support needed to prevent the solid matrix from collapsing. At critical point, the solvent in the gel can diffuse into the surroundings without disrupting the structure of the silica matrix be vented and replaced with air. Once the system is cooled and depressurized, the gel""s solid matrix is left intact. The remaining solid is a network of amorphous particles linked in a superstrong matrix, in the shape of the original alcogel and with approximately the same volume.
3Pardue, Harry and Bodner, George. Chemistry: The Experimental Science. New York, N.Y.: John Wiley and Sons, Inc. Copyright 1995. 
One problem with the supercritical extraction is that organic solvents used in the preparation of the alcogels not only have high critical temperatures and pressures, but are extremely flammable at those conditions and are very dangerous to work with. Arlon Hunt of Lawrence Berkeley National Laboratory demonstrated that a solvent exchange with liquid CO2 can be performed prior to extraction of the solvent from the gel to greatly reduce the danger associated with the extraction process. Carbon dioxide has the benefits of being non-flammable, miscible with organics, and having a low critical point of 31.1xc2x0 C. at 75 atmospheres4. For the supercritical drying to succeed, alcogel must soak in liquid CO2 long enough for the CO2 to completely diffuse through the gel and take the place of the organic solvent. The CO2 can then be brought to supercritical temperatures and pressures for solvent extraction, instead of the organic solvent.
4Weast, Robert ed. Handbook of Chemistry and Physics, 48th Edition. Cleveland, Ohio: Chemical Rubber Co. Copyright 1967. 
Origin of Rayleigh Scattering in Aerogels and Ways to Reduce it
Nearly all silica aerogels exhibit a blue appearance despite being transparent. The blue color is a result of Rayleigh scattering of white light as it passes through the aerogel""s nanopores5. These nanopores, sized from 5 to 150 nm across, are much smaller than the wavelengths of visible light, yet large enough to scatter the higher frequency colors. The larger of these pores scatter visible light more easily. The larger pores ( greater than 15 nm) cause most of the scattering in the aerogel. Shorter wavelengths are diffracted more than longer wavelengths, and therefore blue and violet light are diffracted the most. Although both blue and violet light are diffracted by these nanopores, only a blue color is perceived. This is because the human eye is more sensitive to blue light than any other color, and so violet light scattered by the aerogel is perceived to be mostly blue.
5Hrubesh, Lawrence W. and Poco, John F. Processing and Characterization of High Porosity Aerogels. Lawrence Livermore National Laboratory Reports. (1994). 
The insulative properties of silica aerogel make it an ideal material for insulation for many applications, including the possibility of using it as transparent insulation for windowpanes. The blue scattering in silica aerogel, however, prevents it from being practical in commercial and industrial applications.
It has been proposed by researchers at Lawrence Berkeley Laboratory and the University of Wisconsin that the formation of silica aerogel in microgravity may allow for a greater control over the formation of the silica matrix, narrowing the distribution of pore diameters closer to the 5-15 nm region. The result would be increased ultraviolet scattering and decreased blue-violet scattering, causing the aerogel to appear transparent. To do this, a controllable process is required to allow for the formation of silica aerogel in zero-gravity, and gel times must be adjustable to accommodate for the zero-gravity environments available, for example a KC-135 flight or a drop tower.
Current methods of producing silica aerogel are lengthy, lack fine adjustability, and are expensive. There exist several applications for which inexpensive, controllable production processes are needed. Therefore, it is desirable to develop a process that allows for the production of silica alcogel that is both inexpensive and controllable, which can be followed by an inexpensive procedure to produce aerogel.
1) The objectives of the present invention are as follows: The production of silica alcogel by means of a unique, two-step catalysis procedure that allows for adjustable liquid-to-gel (gelation) times ranging from under 1 second to as long as several hours without formation of opaque species in the gel
2) The production of silica aerogel by means of an inexpensive supercritical drying device made from readily available materials
3) The dry density analysis of aerogels by means of a volumeter
4) The application of the two-step protection process to other related processes including:
a) A process for the formation of silica alcogel using gaseous catalysis
b) A process for laminating aerogel with silica glass or plastic
c) A process for spray-on or sputter application of aerogel
d) A process for the addition of aerogel to microcircuitry
e) A process for the formation silica aerogel microspheres by anti-bubble gelation and theological anti-bubble gelation
f) Application of aerogel as aerogel fibers for use in fabric and clothing
g) Application of aerogel as snap-together aerogel building blocks for constructing larger aerogel structures
h) Application of rapid gelation process in reduced and induced gravity environments
In the method of the present invention, an inexpensive way has been developed to controllably produce silica alcogel in a simple laboratory setting using readily available materials. The resulting procedure allows for the transformation of alcogel solution into gel in times ranging from under one second to several hours (up to 24 hours) using a multiple-step catalysis process, without a need for heat. Other procedures require a minimum of several minutes for gelation, and lose clarity when gelation is induced faster by increasing catalyst concentration or adding heat. In the method of the present invention, alcogels of varying volumes can be formed in a fraction of second without loss of clarity. The invention allows for increased control of the production requirements for the alcogel and production of new, unique aerogel shapes and applications, including the ability to use gaseous catalysis to form thin-film gels.
In the method of the present invention, an alcogel, such as silica alcogel, is prepared by sol-gel gelation. In one method, silicon alkoxide is reacted with water in a dilution solvent and precatalyzed with a basic or acidic catalyst. The solution is allowed to react for a period of time, and catalyzed again to induce rapid gelation. The amount of dilution solvent and catalyst added affects the resulting alcogel""s structure and density. The time delay between these two catalyses affects the gel time of the alcogel solution.
To supercritically dry the alcogels produced by this process and also other alcogels not produced by this process, a manually-controlled supercritical drying device was constructed from welded steel pipes, valves, and gauges. This device is called a manuclave. The aerogels produced by the two-step catalysis show optical clarities comparable to aerogels produced by other similar methods, reduced Rayleigh scattering, and densities of 0.080 g/cm3 to 0.010 g/cm3. In addition, they exhibit reduced Rayleigh scattering when compared to aerogels formed using prior art methods.
Aerogels produced by this method and other prior methods can be analyzed using a dry volumeter that allows for the measurement of an aerogel""s volume without submerging the aerogel under a liquid and thus destroying it.